Laser machining of micro-lenses on the end face of single-mode optical fibers

Focussing of the output beam of optical fibers is required in a variety of applications. We present a laser micro-machining technique for the fabrication of micro-lenses directly on the end face of single-mode silica fibers using a F-2-laser processing station. A uniform ablation spot is projected onto the fiber end face and steered along a trajectory of overlapping concentric circles. The lens profile is controlled by the spot size, the number of circles in the trajectory, and the scanning speed. Strong 157 nm absorption by the silica glass facilitates precise structuring without micro-crack formation in both cases. The surface quality of the fiber-lenses is characterized by AFM and SEM and reveals similar to 100 nm rms roughness with good control of the surface profile. Optical beam profiling indicates the possibility for creating spot sizes of 1/5 the core diameter at the fiber output.